1. Field of the Invention
The present invention generally relates to a display driving apparatus, in particular, to a display driving apparatus with overdriving mechanism.
2. Description of Related Art
When a liquid crystal display (LCD) displays an image data, a driving voltage is supplied on each pixel to rotate the liquid crystal molecules in the pixel and accordingly change the transmissivity of the pixel, so that the pixel can display desired brightness and color. The rotation rate and angle of the liquid crystal molecules are related to the value of the driving voltage, namely, the higher the driving voltage is, the larger the rotation rate and the angle in stable state are.
To meet the display rate of the LCD and prevent residual image while displaying dynamic images, an overdrive value has to be supplied on the pixel so that the rotation of the liquid crystal molecules can be driven to another angle in a specific period of time while displaying the next image. In this way, the rotation speed can be raised. The overdrive value corresponding to a particular gray scale value can be located in a lookup table (LUT).
FIG. 1 is a block diagram of a conventional overdriving apparatus. Referring to FIG. 1, the memory unit 110 stores the pixel data of a previous frame F1. The display accelerating unit 120 receives the pixel data of a current frame F2 and reads the pixel data of the previous frame F1 from the memory unit 110. Then the display accelerating unit 120 locates an overdrive value SOD of the display pixels in a LUT disposed therein for accelerating the display of the image.
For example, if the pixel data of the previous frame F1 is to rotate the liquid crystal molecules of a particular pixel 30°, but the pixel data of the current frame F2 is to rotate the liquid crystal molecules of the pixel 150°, then the display accelerating unit 120 outputs the overdrive value SOD through table lookup after it receives the pixel data of the current frame F2 and the pixel data of the previous frame F1. With the overdrive value SOD output by the display accelerating unit 120, a larger voltage is supplied on the liquid crystal molecules so that the liquid crystal molecules can be transited and rotated to 150° more quickly in the interval between two images, and accordingly the response time is increased.
However, along with the increment in the resolution of LCD, the quantity of display data in the pixel data of the previous frame F1 stored in the memory unit 110 is also increased considerably, and accordingly the cost of the memory is greatly increased. Thereby, the display data in the pixel data of the previous frame F1 should be compressed to reduce the quantity thereof before it is stored and decompressed while it is used, so that the requirement to the memory volume can be reduced.